COMPARATIVE RESPONSES OF GENETICALLY LEAN AND FAT CHICKENS TO LYSINE, ARGININE AND NONESSENTIAL AMINO-ACID SUPPLY .1. GROWTH AND BODY-COMPOSITION

1. Three experiments were performed to study the effects of amino acid imbalance on the growth of genetically lean (LL) or fat (FL) male chickens from 28 to 42 d of age. In experiment 1, five concentrations of digestible lysine were compared (4.75, 6.75, 7.75, 8.75 and 9.75 g/kg). In experiment 2, four concentrations of digestible arginine were compared (6.53, 7.69, 8.84 and 10.0 g/kg). In experiment 3, three diets were compared: a high-protein diet (189 g CP/kg), a low-protein diet containing added essential amino acids (EAA) (144 g CP/kg) and this low-protein diet supplemented with 40 g/kg of non-essential amino acids (NEAA) (glutamic acid + aspartic acid). 2. LL birds exhibited a lower growth rate than the FL when the diet was deficient in either lysine or arginine. Plotting weight gain against lysine or arginine intake suggested that most of this effect was caused by variations in food intake. 3. When protein gains (body or total proteins) were plotted against lysine or arginine intake, LL chickens appeared more efficient than FL chickens. 4. Similar growth rates, although slightly lower in FL, were obtained with low- and high-protein diets. However, NEAA supplementation of the low-protein diet reduced adiposity of LL and did not modify that of FL. Increasing crude protein content (all amino acids) was more effective than NEAA supplementation in decreasing the adiposity of both lines.